It is desirable to reduce the peak-to-average power ratio (PAPR) in frequency division multiplexing and orthogonal frequency division multiplexing (OFDM). Several techniques aiming to achieve this purpose are known. A summary of these techniques can be found in Tao Jiang, and Yiyan Wu, “An Overview: Peak-to-Average Power Ratio Reduction Techniques for OFDM Signals,” IEEE Transactions on Broadcasting, Vol. 54, No. 2, June 2008. Relevant techniques can be divided into three groups. Another overview paper provided by Seung Hee Han and Jae Hong Lee is entitled “An overview of peak-to-average power ratio reduction techniques for multicarrier transmission,” and was published in IEEE Wireless Communications, Vol. 12, 2005. Both these documents are incorporated herein in their entireties by this reference.
A first group of peak-to-average power ratio reduction methods segment OFDM symbols into blocks. These blocks are processed independently to reduce their respective peak-to-average power ratio by applying phase rotation to the symbols on a per sub-carrier or group basis. Alternatively all of the OFDM symbols can be multiplied by a phase rotation vector or various bit interleavers can be tested to find those that provide the best peak-to-average power ratio. All these methods require the receiver to know the multiplying phase vector, the partitioning sequence and/or the interleaver in use. The main techniques in this group are Selective Mapping (SLM) scheme and a Partial Transmit Sequence (PTS) scheme.
Other methods rely on the modification of the symbol constellation used to encode the data bits. This is done by generating a set of sub-symbols related to a particular constellation symbol. These symbols are tested on a per sub-carrier basis until a satisfactory PAPR reduction is obtained. Again, some of these methods require informing the receiver about the modifications made per sub-carrier. An exemplary technique is constellation shaping.
Other techniques rely on the use of OFDM sub-carriers, or tones, that can be dynamically allocated or modified to reduce peak-to-average power ratio. The Tone Reservation (TR) and Tone Injection (TI) techniques are examples of this.
All the above techniques share the same underlying concepts of requiring a modification of data to achieve peak-to-average power ratio reduction before a time domain signal is transmitted.
S. H. Muller and J. B. Huber disclose a method in which the OFDM symbols are required to be segmented into blocks in “OFDM with reduced peak-to-average power ratio by optimum combination of partial transmit sequences,” Electronics Letters, 27 Feb. 1997, Vol. 33, No. 5, the entirety of which document is incorporated herein by this reference. S. H. Han and J. H. Lee discuss a method in which constellation symbols need to be defined prior to transmission in “Peak-to-average power ratio reduction of an OFDM signal by signal set expansion,” IEEE International Conference on Communications, 2004, Vol. 2. This technique is based on signal set expansion in which each point in an original signal set is associated with two or more points in an expanded signal set. Each symbol in an OFDM data block is mapped into a point among associated points in the expanded signal set so as to achieve peak to average power reduction.